Distance and depth finding



July 30, 1935. E. E. TURNER, JR 2,009,459

DISTANCE AND DEPTH FINDING Filed July 29, 1929 A T TORNEY Patented July 30, 1935 UNITED STATES PATENT @FFEQE I Edwin E. Turner, In, West Roxbury, Mass., as-

signor to Submarine Signal Company, Boston,

I. Mass., a corporation of Maine Application July 29, 1929, Serial No. 381,970

11 Claims. (01. 177-386) The present invention relates to a system for determining distances and depths by measuring the time interval between the emission of a sound or energy impulse and the return of its echo.

This has been done in the prior art in a number of different ways, most of which have been successful. Perhaps the most successful of these systems are those in'which the sound impulse is emitted when a rotating indicator is at a zero position with reference to a scale and the incoming echo which is received by a sound receiver operates the indicator, thereby indicating with reference to the scale the distance or depth. In

these systems the sound emitter is usually controlled by the rotating indicator, or something connected to it. Further, this method demands that the indicator be rotating continuously and that the speed be maintained constant. While it has been found to be possible to do this satisfactorily and without much trouble, it is, nevertheless, true that the indicator device and the mechanism to control the proper times of sound emission have been somewhat large and expensive.

In addition, while these systems usually give a substantially continuous indication of distance or depth, since the periodic depth or distance indications are very close together (about a second apart) nevertheless the operator must watch for one of these indications to know what the depth or distance is. a

In the present system, the indicator does not move continuously, but assumes the correct position of depth with reference to a scale and remains at that position until the depth changes, at which time it moves to its new and proper position. The apparatus is much simplified over that of the prior art and, in addition gives an absolute, continuous indication at all times.

In preference to having the indicator control the times of emission of the sound impulse, in the present inventionthe sound emitter operates independently and at each emission sets the time measuring circuit in operation. This time measuring circuit is entirely electrical, has no moving parts, and operates an indicator, which likewise moves only with a change of successive time measurements.

The invention is applicable to all types of distance measurement or measurement of time intervals, but finds perhaps its greatest and most important application to depth sounding and height measurement, the former in the water with an impact sound emitter and a hydrophone as a receiver, and the latter with similar apparatus designed for 'use in air.

The invention will now be described in detail in connection with the drawing, in which Figure 1 shows an embodiment of the invention and Figure 2a modification.

In the drawing, the sound or energy impulse is emitted by an impact excitation of the diaphragm l by the striking of the diaphragm by the hammer I at the end of the arm 5 of the lever pivoted at 6. The hammer is operated by a motor 2 tuming by means of a worm H the cam 3, which has a pin 4 extending perpendicularly from the cam surface. The pin 4 catches under the lower side of the arm 28 of the pivoted lever and raises the arm against the force of the spring 8. When the pin 4 has passed beyond the arm 28, the armis released and the spring 8 forces the hammer 1 against. the boss of the diaphragm I, thereby emitting a sound impulse. The sound travels to the surface 29, is reflected and picked up by the hydrophone or receiver 22, which may be amplified by the amplifier 23.

The amplifier is preferably of the type disclosed in my copending United States application Serial No. 270,660, filed April 17, 1928, which is very desirable for operating the relay 24. In the drawing this is shown as a mechanical relay, but it may be of any other suitable type. The circuit of application Serial No. 270,660 furnishes a dellnite and'uniform collapsing current for all signals received, so that the relay 24 will have a uniform operation, particularly with regard to time lag, which is important, as will be explained later.

When the arm 28 is released, the contact lever 9 follows with it and is so set that the contact between 9 and I is broken at the time when the hammer 1 strikes the diaphragm I. The battery 12, which must be of standard and substantially unvarying voltage, or one on which the voltage is controllable to obtain a definite voltage, before the opening of the contact between 9 and I0 keeps the condenser I 3 at a definite potential. After the circuit is broken, the condenser l3 discharges through the constant resistance M at a rate determined by the formula -where V0 is the initial voltage on the condenser From theabove it-will be noted that the time interval "t" is measurable by the voltage Vt on circuit operates, causing the relay 24 to release thearm 26, which flies back, due to the pull of the spring 25 making a contact between 26 and 21.

This, it will be noted from the drawing, places the condenser I5 at the same potential as .the condenser I3 and charges the grid of the tube IS with the same potential with respect to the filament.

The relay 24 does not remain in this position. It is immediately drawn back, breaking the contact between 26 and 21, thus isolating the charge on the condenser I5 and on the grid of the tube I6. The vacuum tube I6 has a definite plate current dependent upon the voltage of the battery 2| and the grid potential of the tube. With a constant plate voltage the current varies solely with the grid potential, so that the plate current may be made afunction' of the grid voltage, which in turn is dependent upon the charge on the condenser I3 at the time the contact between 26 and 21 is closed. Since the charge on the condenser I3 is a function of the time counted from the emission of the sound signal causing the opening of the contact between 9 and III, the charge on the condenser I3 at the time the contact between 26 and 21 is closed by the returning echo isa measure of the time interval between the emission of the sound and the receiptof the echo. This charge is measured by the plate current flowing through the vacuum tube I6 by ,means of the ammeter l1 and the recording ammeter I8. If it is desired, a relay I9, operated on a definite current value, may be ,used to operate the alarm 20. i

When.the echo has arrived closing the contacts of the relay 24 momentarily, the needle of the meteri1 will-assume a definite position dependent upon the potential of the grid I6. The contact opening instantly, this charge remains on the grid I6, since it cannot leak off, and the needle of the meter I1, therefore, keeps its position.

In effect, the circuit including the vacuum tube I6 and themeter I1 may be called a vacuum tube voltmeter, since it measures the potential on the grid of the tube I6.

The operation 5 repeated each time a signal is emitted. If the epth should change, the charge on the condenser l3 would be different at the time the relay contacts were closed and thus the grid potential would be changed and the plate current in the tube IS. The needle of the meter I1 would then assume a different position corresponding to the newly measured depth. In other words, the position of the needle of the meter I1 would not change until a new sounding indicated a different depth. The last sounding depth or distance measurement can therefore be read at any time from the position of the needle of the meter I1.

The grid of the tube I6 is used as a floating grid since it is free from the ordinary plate current in the circuit and assumes a potential dependent only upon the charge that is'applied to it. It should also be noted that this grid is brought to the proper potential not through a single charge of the condenser I5, but because of successive periodic operations which bring the grid alternately to its proper value. The condenser I6 is comparable in'size or larger than the condenser It used in the timing circuit, but the condenser I3 is not discharged to any appreciable extent across the condenser I6 because of the fact that the potential is applied to the condenser I5 only for a very short time. In actual practice soundings are made at intervals of about one second, and under this manner of operation it isnecessary to have probably four or five soundings before the true sounding is established. When the condenser II is once charged to the potential established by a previous sounding, the following measurement is not so far different but what the correct reading is currently established.

It should be'noted that in the present system the direct signal proceeding directly from the diaphragm I to the hydrophone 22 cannot cause a great disturbance of the readings, as the echo always follows and corrects the potential of the grid I6. Even though the direct signal will operate the meter I1, it will be only for sucha short time that for the most part the meter will always read the depth. It should also be noted that operation by the direct signal will not make the circuit inoperative when the echo comes in, as would be the case if the effect of producing the indication caused. a discontinuance of the discharge of the condenser I3.

Figure 2 shows a slight modification of the circuit of Figure 1 in which the point of measurement is determined not when contact is made ,between 26 and 21 but when the contact between 26 and 30 is opened. In this manner the time element of the relay is substantially eliminated-as the opening of the circuit is practically instantaneous.-

The feature of the circuit shown in Figure 2 h another advantage. In sounding by the echo method the echo is usually powerful in shallow water and weak in deep water. The receiving cir-.

cuits heretofore used had to be sensitive enough for deep water and when so adjusted were often too sensitive for shallow water, with the result that direct signals and other noises incidental to the emission oi the signal often caused the operation ofthe indicator and thereby produced erroneous readings.

In the system shown in Figure 2 this is eliminated by making the circuit of such a sensitivity that as the time interval necessary for the echo to return becomes greater the sensitivity of the receiving circuit becomes greater. In deep water, therefore, the circuit is more sensitive than in shallow water.

In the operation of this circuit it may be noted that the transformer does not change the poten- 'tial on the condenser I3 since the filament grid circuit of the tube 3| has practically an infinite impedance and therefore there is no way of applying the voltage on the secondary of the transformer 32 across the condenser I3. The two potentials, that across the condenser I3 and that across the secondary of the transformer 32, are always in series.

As in Figure 1, when the sound is emitted the contact between 9 arid I0 is broken and the charge accumulated on the condenser I3 is allowed to discharge through the resistance I. At the same time, however, the condenser I3 is connected continually between the grid and the filament of the tube 3 I, which is the first tube 01' the receiving cir cuit. Across the hydrophone 22 is a transformer 32 which has its secondary connected in the filament grid circuit of the tube 3 I potential generated by the received signal sumciently overcomes the charge on the grid placed there by the condenser l3 to allow the circuit to operate. If the signal returns immediately, as when the direct signal travels to the receiver without being reflected, the charge on the condenser l3 will not appreciably have leaked ofl.

In this way the grid of the tube 8| is highly negative and the direct signal, even though powerful, will not generate sufiicient voltage to overcome this high negative charge and operate the .circuit.

0n the other hand, if the water were deep the charge on the condenser I3 will have appreciably leaked off and the grid of the tube 3| will be less 29 negative so that a smaller signal voltage will operate the circuit. The circuit beyond the tube 3| is like that shown and described in my copending application Serial No. 270,660 above referred to, with the exception that the relay 24 replaces the indicating neon tube. The echo passing through the circuit energizes the relay 24 and opens the contact between 30 and 26, thereby isolating the charge on the condenser l3. The instant of the opening of the contact 313V and fixes the measurement of the time interval as the condenser |3 no longer loses its charge after the opening and, therefore, whatever the time elapsing until 26 and 21 contact, thetime measurement is unaflected. The making of the contact between 26 and 21 places the charge of the condenser 58 on the grid of the tube l6, which produces the indication on IT, as explained above.

It should be noted that the sensitivity of the receiving circuit is a function of the time interval between the emission of the direct signal and the receipt of the echo, and that the deeper the water, the more sensitive the receiving circuit becomes.

Having now described my invention, I claim:

1. In a system for measuring depths by the echo method in which periodically repeated sound signals are produced at close intervals of time, a sound receiving system including a sound receiver, a valve receiving circuit having a valve with anode, cathode and a control grid, indicating 0 means in the anode-cathode circuit adapted to ive a continuous indication which varies as a function of grid potential, means providing a potential varying in intensity from the time the 55 impulse is emitted and means operated by the receiver on the receipt of an echo for impressing on said control grid said varying potential for establishing a bias for the following echo signal.

2. In a system for measuring depths by the echo method in which periodically repeated sound signals are produced at close intervals of time, a sound receiving system including a sound receiver, a valve receiving circuit having a valve with anode, cathode and a control grid, indicating means in the anode-cathode circuit adapted to ive a continuous indication which varies as a function of grid potential, means providing a potential varying in intensity with the depth being measured and means for impressing onsaid control grid periodically said potential as a varying bias, said last-mentioned means being operated by the sound receiver to impress the said potential upon the control grid upon the receipt ,of the sound impulse by the soundreceiver.

3. In a system for measuring depths, in which ing a sound receiver, means including a potential source varying definitely as a time function from the periodic production of the sound signal, means for measuring the magnitude of the potential source and means operated by the sound receiver for impressing momentarily periodically upon receipt of the echo the potential source upon the measuring means. 4

4. In a system for measuring depths, in which a sound signal is periodically produced at close time intervals, a sound receiving system including a. sound receiver, means including a potential source varying definitely as a time function from the periodic production of the sound signal, means for measuring the magnitude of the po.-- tential source and means operated by the sound receiver for impressing periodically for momentary intervals the potential source on the measuring means to establish the measured.

5. In a system for measuring depths, means for periodically producing a sound signal, a sound receiving system including a sound receiver, means including a potential source varying definitely as a time function from the periodic production of the sound signal, means for measuring the magnitude of the potential source including a vacuum tube circuit having a vacuum tube with a control grid, a cathode and anode, said control grid being coupled to said cathode through a condenser, means periodically operated by the receiving system on the receipt of the reflected echo to impress the potential source upon said control grid to establishby successive impressions a poprising an electric circuit including means pros.

viding a predetermined electrical potential for the circuit, means varying as a function of time when the predetermined potential is withdrawn from the circuit, means for withdrawing the same synchronously with the sending of the impulse, means for receiving the reflected echo and means operated thereby, marking the end of the elapsed time to be measured, including a thermionic tube circuit having, as an input control, a themiionic tube with a free grid with means for connecting the grid upon receipt of the echo to said electrical potential and means operated by the electrical potential assumed by said grid to indicate the measure of the time interval as a function of the electrical potential.

7. In a system for measuring depth by the elapsed time method between the sending of an impulse and the receipt of a reflected echo, means for measuring the time interval including a condenser and means for discharging the condenser at a known rate from the beginning of the time interval marked by the sending of the impulse, means for receiving the reflected echo and means operated thereby for measuring the potentiaLof the condenser at the end of the time interval to be measured as a function of the time interval, including a vacuum tube voltmeter having a float-. ins rid and means operated by the receiver upon potential to bereceipt of the reflected echo for momentarily conrecharging the condenser before the sending of the impulse.

8. In a system for measuring depths by the.

elapsed time method between the sending of an impulse and the receipt of the reflected echo, means for measuring the time interval comprising an electric circuit including means providing a predetermined electrical potential for the circuit, means varying as a function of the time when the predetermined potential is withdrawn from the circuit, means for sending a signal impulse periodically at short intervals, means for withdrawing the predetermined potential synchronously with the sending of the impulse, means for receiving the reflected echo and means operated by the receiver for marking the end of the elapsed time to be measured including a thermionic tube circuit having as an input control a thermionic tube with a free grid with means for connecting the grid upon receipt of the echo to said electrical potential and means operatedupon the application of said potential to said grid to indicate the measure of the time interval as a function of the electrical potential, said transmitted impulses being produced periodically and at sufficiently short periods so that the charge I on the grid remains substantially constant bethe'measuring interval including a vacuum tube voltmeter having a floating grid and meansfor applying the potential intermittently at close time intervals to said floating grid at that moment. I

10. In a system for depth measurement, a time measuring circuit including. means establishing an initial potential at the beginning 'of the interval to be measured, means for causing the potential to vary thereafter as a function of time from the moment of establishment of the potential, and means for measuring -the potential at the end of the measuring interval including a vacuum tube voltmeter having a floating grid and means for applying the potential intermittently at close time intervals to said floating grid 7 'at that moment comprising a relay adapted to make momentary contact between the potential source and the floating grid.

11. In a system for measuring depths by the echo method in which periodically repeated sound signals are produced at close intervals of time, a sound receiving system including a sound receiver, a valve receiving circuit having a valve with anode, cathode and a control grid, indicate ing means in the anode-cathode circuit adapted to give a continuous indication which varies as a function of grid potential, means providing a potential varying in intensity as a function of the depth being measured and means for impressing on said control grid periodically said potential as a varying bias, said last-mentioned means being operated by the sound receiver to impress the said potential upon the control grid upon the receipt of the sound impulse by the sound receiver.

EDWDI E. TURNER, Jia 

